Storage hoppers are utilized for transporting various types of granular materials, including grains, animal feeds, crushed rock, coal, fertilizers, sand, salt, and other granular materials. Such storage hoppers include openings or apertures for releasing the granular materials. These apertures are generally closed with a trap door type mechanism. However, an operator may have to exert a great deal of effort to engage the release mechanism or device. For example, in some instances, storage hoppers may be filled with a large volume of material that exerts a great deal of weight on a door. Further, materials transported in such hoppers may themselves weigh a great deal, such as rock. Thus, opening a door to release these materials may require a great deal of effort on the part of an operator to overcome the friction generated by the weight of the material upon the door and its supporting structure. This difficulty may be compounded by adverse environmental conditions: oftentimes, an operator will deliver materials at night, as well as in all types of weather conditions, including cold weather, rain, snow, and the like.
In order to increase the ease with which an operator may open a door on a storage hopper, some types of doors have been provided with mechanisms designed to reduce the amount of friction on a door and/or to provide mechanical advantage for opening the door. Such doors may include various types of mechanisms, including rack and pinion mechanisms, flexible drive belt mechanisms, doors set on an inclined plane, and the like. However, such mechanisms may be exposed to wear and tear during the course of operation, both due to the forces on the mechanisms as well as the granular nature of the material being transported. For example, material may become lodged in a rack and pinion system and wear out the gearing over time. Further, with a flexible belt system, the belts may become stiff and/or may stretch over time, especially in cyclically changing weather conditions. Still further, doors set on an inclined plane may intrude into the space below a storage hopper, impeding material delivery.
Thus, it would be desirable to provide a door assembly for a storage hopper which did not intrude into a space below the hopper, which was particularly capable of opening and closing in various weather conditions and under various load conditions, which was capable of containing and releasing various types of materials, which provided different rates of discharge for the materials, and which was economical to manufacture.